Five-fingered hand devices which mimic a human hand are recently known. The five-fingered hand device of this type includes a base having a palm and a back, and a thumb mechanism, an index finger mechanism, a middle finger mechanism, a ring finger mechanism, and a little finger mechanism which correspond respectively to the five fingers of a human being. Each finger mechanism has a plurality of joints and is rotatable at each joint, so that it is able to perform bending and stretching operations (see Japanese Patent Application Laid-Open No. 2008-183629).
In the conventional hand device, a plurality of motors are used as drive units for driving the bending and stretching operations of the finger mechanisms. That is, each finger mechanism is provided with three joints, and the motors for moving the joints are arranged in the base. Wires are used to connect the motors with the finger mechanisms. As the motors cause the finger mechanisms to bend or stretch via the wires, a grasping operation and other operations are performed by the finger mechanisms.
In order for the motors to be housed in the base, however, the motors need to be relatively small in size. As a result, sufficient driving forces may not be obtained from the motors, or even when the motors can bend and stretch the finger mechanisms, a sufficient grasping force may not be obtained from the finger mechanisms.
To obtain a sufficiently large grasping force, it is conceivable to adopt motors having a relatively large driving force. In this case, however, the motors will be increased in size as well as in weight, leading to an increase in size of the base and the finger mechanisms. This hinders reduction in size and weight of the five-fingered hand device so as to approximate the size of a typical human hand, making it difficult to adapt the hand device to a humanoid robot having a build and shape equivalent to those of a human being.